1. Field of Invention
The present invention relates to a centrifugal fan. More particularly, the present invention relates to a centrifugal fan with a noise reduction functionality.
2. Description of Related Art
As notebook PCs become thinner, less space is available for heat convection and heat dissipation components inside the notebook PC case housing. High-frequency components, such as the CPU (central processing unit) and graphics processing chip, also place limitations on heat dissipation designs. Thus, the mainstream method to dissipate heat is forced heat convection via a centrifugal fan.
A centrifugal fan employs a spiral-shaped flow channel design to convert dynamic air energy into static pressure so as to overcome the high air flow impedance inside the notebook PC case housing. However, high static pressure generating centrifugal fans face the dual challenge of reducing noise and improving heat dissipation efficiency. Noise can be divided into broadband noise and narrowband noise, wherein narrowband noise is preferably eliminated from a centrifugal fan.
FIG. 1 illustrates a perspective view of a conventional centrifugal fan. A centrifugal fan 100 includes a spiral-shaped housing 102, which has a motor (not illustrated) and an internal centrifugal impeller 108. The motor is mounted behind the base 106, and three support brackets 104 links the base 106 to the remaining parts of the spiral-shaped housing 102. Three void spaces are formed between the three support brackets 104, the base 106 and the remaining parts of the spiral-shaped housing 102. When the motor rotates the centrifugal impeller 108, driven airflow is sucked along a direction 110 and then into the spiral-shaped flow channel through the void spaces. The driven airflow, which travels at a rate of 15-40 km/hr with relation to the spiral-shaped housing 102, is unavoidably incident into the support bracket 104. Crashing impacts against the support bracket 104, which perpendicularly links to the base 106 and the spiral-shaped housing 102, generates high-frequency, narrowband noise.